The present invention relates to a refractory structure having an external casing covering the cold end face of a refractory brick, the structure having particular use in lining furnaces. The invention also relates to a method for more effectively sealing off the cold-end face of a refractory brick.
Workers in the steel industry have established that magnesite-carbon brick, when used in electric arc furnace hot spots, slag lines, and side walls, performs better and is cheaper than previously-used fused cast material. Specifically, magnesite-carbon brick, while giving the same number or more heats as fused cast material, requires significantly less gunning maintenance.
A vexing problem, however, is that the cold-end face of magnesite carbon brick oxidizes when exposed to oxygen at service temperatures over about 1000.degree. F. At even higher temperatures, the oxidized brick, no longer possessing the original carbon-pitch bonding system, crumbles easily, causing deterioration of the brick lining from the cold end, i.e. hidden end. More brick is required, increasing the cost per ton of steel.
Inner lining deterioration, hidden from human view, is, of course, extremely dangerous to steel workers. Further, because such inner, hidden deterioration renders it impossible to determine accurately how much furnace lining is remaining, furnace operators lose the ability to determine visually how long a particular lining will last.
As an engineering matter, eliminating air infiltration into the area between the cold-end faces of the bricks and the shell of the electric arc furnace is difficult. In service, furnace shells frequently warp, preventing tight abutment of the brick lining. Brick separation from the top of a furnace shell, rendering top bricks extremely vulnerable to oxidation, is also common. Further, shells often have numerous holes for a variety of reasons.
Convinced that air infiltration is inevitable, workers in the art have attempted to solve the cold end-face oxidation problem by chemically or mechanically sealing off the cold end face of refractory bodies, such as magnesite carbon brick. Various forms, however, of chemical coatings, sealers and powders have not satisfactorily increased the service life of magnesite carbon brick.
In an attempt to reduce contact between air and the cold end face of refractory bodies mechanically, workers have used a metal plate on the cold end face of a brick while additionally wrapping a metal sheathing around two or more adjoining side faces. Gaps between the plate and the sheathing at the edges of the cold end face, however, admit some oxidizing air, regardless of whether the plating is attached simultaneously with, or after, molding of the brick. Accordingly, this method of sealing off the cold end face is still not entirely satisfactory.
The use of either aluminum or steel foil to wrap the end of a brick prior to plating has been suggested as a viable solution. Predicted cold end face service temperatures, however, exceed the melting point of aluminum, while steel foil is disadvantageous because it tends to cut workers. Artisans have accordingly continued a vigorous search for a brick less prone to oxidize at the cold end face in order to reduce the cost per ton of steel.